Streaming of movies would be supported however the movie files maybe important as the higher the video quality is, the more bandwidth will be taken and used on the LAN port. I presume maybe one 1080p file would work well, maybe two streaming. Not sure. I haven't tried to stream more than one at a time and I have a DNS-345 and use a Boxee box and can stream raw blue ray files contained in MKV files. Also HDD drive speeds can be important as well.
Might do a search in this forum to see if anyone else mentions video streaming problems. I've seen some performance issue posts with this model DNS.